SATA, Gain or Pain?

Clarifications

For a start your HDDs are [b]NOT[/b] 'GT/s'. they are '[u][b]Gb/s[/u][/b]' - GIGABITS per second.

Your cited transfer rates of '70MB/s' is for [b]MEGABYTES[/b] per second. There are [u]EIGHT[/u] bits in a byte. Thus the transfer rate is [b][u]560Mb/s. - MEGABITS per second.[/u][/b]

The rated speed for SATA is 300MB/s [which equates to 2.4Gb/s data throughput] and today's mechanical hard disk drives can transfer data at up to 127 MB/s so you are doing rather better than you think you are. ;)

You'll have to pay closer attention to the differences between '[u][b]B[/u][/b]' and '[u][b]b[/u][/b]'. :)

First, when transferring between two devices, you will max you speed at the SLOWER device, because the transfer will only go as fast as the slowest device.

Secondly, when less data is sent the faster it will appear to go. Because the information the OS generates are just time and speed estimations based on how much data or how many files being transfers. Less data equals rougher estimates.

One more thing to take into account is that the rated transfer speeds are measured in a lab with direct transfer between a hard drive and a data buffer. Fully ideal optimized conditions. But, nowhere near "real world".

When you transfer data between 2 hard drives on a computer at least some part of the data path is shared. Thus, once your file size exceeds the of the smallest data buffer in the path, the transfer rate drops and will eventually be the slower of about 1/2 the data rate of the fastest device in the data path, or the data rate of the slowest device.

The worst case for data transfer between 2 similar devices is when they are both connected to the same drive controller on the motherboard. That is part of why it was best practice for PATA IDE systems to have the hard drive on 1 IDE cable and the optical drives on another.

Chas